1. Field of the Invention
This invention refers to a highly sensitive measuring cell for a differential refractometer of the interference type or other type of detector for chemical analyzers.
2. Description of the Prior Art
It is known that an indicator of the concentration of a liquid or gaseous sample can be obtained by measuring its refractive index. However, with increasing requirements for measuring low concentrations it becomes more and more important to maintain the temperature and the pressure constant. Nevertheless, as the concentration is decreased a limit is soon reached, beyond which it is not possible to maintain the temperature and pressure constant by conventional methods.
By performing differential measurement on the basis of a known sample and an unknown sample, it is possible to drastically reduce the constant temperature and pressure requirements, as both of the samples subjected to measurements are affected by temperature and pressure to an equal degree. Various types of refractometers which are based on this principle are available, and they may for example either utilize two prismatic cells for the samples or may utilize two cells for measuring total reflection, with the last-mentioned cells being disposed such that when the same refractive index exists in the two cells the deflection of light passing through the cells will not be affected. These refractometers are of the diffraction type.
In recent years a refractometer of the interference type has also entered the market. This refractometer operates by measuring the velocity of light through the measuring cell and through the reference cell whereafter the difference in velocities is determined. In this manner it becomes theoretically possible to increase the sensitivity to a great extent in consequence of the signal to noise ratio of a refractometer operating on the interference principle being high, but of course the requirements with regard to the measuring cell will become higher to a corresponding degree.